Light driving systems have been available for many years and come in many different configurations. Many light systems are driven directly by AC input signals transformed from an AC mains input signal from a power distribution grid to a residential or commercial building. However, some lighting systems (e.g., Light Emitting Diodes (LEDs)) are driven by a DC input signal, so the AC input signal needs to be converted to a DC input signal. The DC input signal can be provided by rectifying an AC input signal and providing the rectified AC input signal to an AC/DC converter, for example, such as a switching regulator. Between the power distribution grid and the switching regulator in a modern electronic system are many elements, including a power transformer outside of the building, a wire connecting the AC input signal to the electronic system, the circuit breaker or fuse, lightning arrestors, an EMI filter and possibly many other elements. These elements are predominantly reactive, with inductive and capacitive components. The input impedance of a switching regulator can be purely resistive, reactive or even exhibit negative resistance. The series connection of these elements and the regulator can cause resonance which can result in voltage and current ringing by one or more input components, such as the EMI filter. In the most benign cases, this ringing results in extra EMI and power loss. But in more extreme cases, this ringing can result in false operation of the switching regulator.
In lighting systems, another element can be added between the mains and the load known as a light dimmer, which adjusts the brightness of the light. Light dimmers are abundant and set thresholds in which to begin conduction of the AC input signal to a light. This element contains reactive elements but also a semiconductor switch, such as a TRIAC or MOSFET. The discontinuity of the semiconductor switch adds another aspect to the problem. That is light dimmers were designed to drive incandescent lights, which draw current all of the time. However, a switching regulator does not draw current all of the time. This results in transient effects due to fast turn on voltage at the output of the dimmer, which causes ringing of the input stage components (e.g., EMI filter, input capacitors). Ringing of input stage components can cause commutation of the dimmer solid state switch, thus defeating the dimming function and confusing the controller that is attempting to monitor the output behavior of the dimmer.